1. Field of the Invention
The present application relates to a paperboard plate having a plurality of side walls and a plurality of corner walls.
2. Description of Related Art
Consumers desire a receptacle for foodstuff that is inexpensive and disposable, yet provides properties comparable to more costly nondisposable receptacles for foodstuff. Manufacturers are challenged to produce a disposable receptacle with properties acceptable to consumers at lower costs. Specifically, consumers desire and manufactures seek to provide disposable foodstuff receptacles having sufficient rigidity to support foodstuff held therein at the lowest cost possible.
Conventional paperboard plates are made from a suitable feedstock material by way of a variety of processes employing many types of equipment. Such materials, techniques and equipment are well known to those of skill in the art.
Paper disposable food containers may be made by way of pulp-molding processes or by way of pressing a planar paperboard container blank in a matched metal heated die set. Pressed paperboard containers may be made as noted in one or more of U.S. Pat. No. 4,606,496 entitled “Rigid Paperboard Container” of R. P. Marx et al; U.S. Pat. No. 4,609,140 entitled “Rigid Paperboard Container and Method and Apparatus for Producing Same” of G. J. Van Handel et al.; U.S. Pat. No. 4,721,499 entitled “Method of Producing a Rigid Paperboard Container” of R. P. Marx et al.; U.S. Pat. No. 4,721,500 entitled “Method of Forming a Rigid Paper-Board Container” of G. J. Van Handel et al.; and U.S. Pat. No. 5,203,491 entitled “Bake-in Pres-Formed Container” of R. P. Marx et al. Equipment and methods for making paperboard containers are also disclosed in U.S. Pat. No. 4,781,566 entitled “Apparatus and Related Method for Aligning Irregular Blanks Relative to a Die Half” of A. F. Rossi et al.; U.S. Pat. No. 4,832,676 entitled “Method and Apparatus for Forming Paperboard Containers” of A. D. Johns et al.; and U.S. Pat. No. 5,249,946 entitled “Plate Forming Die Set” of R. P. Marx et al. The forming section may include a plurality of reciprocating upper die halves opposing, in facing relationship, a plurality of lower die halves. The upper die halves are mounted for reciprocating movement in a direction that is oblique or inclined with respect to the vertical plane. The paperboard blanks, after cutting, are gravity fed to the inclined lower die halves in the forming section. The construction of the die halves and the equipment on which they are mounted may be substantially conventional; for example, as utilized on presses manufactured by the Peerless Manufacturing Company. For paperboard plates stock of conventional thicknesses, i.e., in the range of from about 0.010 to about 0.040 inches, it is preferred that the spacing between the upper die surface and the lower die surface decline continuously from the nominal paperboard thickness at the center to a lower value at the rim.
The paperboard which is formed into the blanks is conventionally produced by a wet laid paper making process and is typically available in the form of a continuous web on a roll. The paperboard stock is preferred to have a basis weight in the range of from about 100 pounds to about 400 pounds per 3000 square foot ream and a thickness or caliper in the range of from about 0.010 to about 0.040 inches as noted above. Lower basis weights and caliper paperboard is preferred for ease of forming and realizing savings in feedstock costs. Paperboard stock utilized for forming paper plates is typically formed from bleached pulp furnish, and is usually impregnated with starch and double clay coated on one side as is further discussed herein.
In a typical forming operation, the web of paperboard stock is fed continuously from a roll through a cutting die to form circular blanks which are then fed into position between the upper and lower die halves. The die halves are heated to aid in the forming process. It has been found that best results are obtained if the upper die half and lower die half—particularly the surfaces thereof—are generally maintained at a temperature in the range of from about 250 degrees F. to about 400 degrees F. These die temperatures have been found to facilitate the plastic deformation of paperboard in the rim areas if the paperboard has the preferred moisture levels. At these preferred die temperatures, the amount of heat applied to the blank is sufficient to liberate the moisture within the blank and thereby facilitate the deformation of the fibers without overheating the blank and causing blisters from liberation of steam or scorching the blank material. It is apparent that the amount of heat applied to the paperboard will vary with the amount of time that the dies dwell in a position pressing the paperboard together. The preferred die temperatures are based on the usual dwell times encountered for normal plate production speeds of 40 to 60 pressings a minute, and commensurately higher or lower temperatures in the dies would generally be required for higher or lower production speeds, respectively.
Paperboard for disposable pressware typically includes a coating. Illustrative in this regard are U.S. Pat. No. 5,776,619 (“the '619 patent”) to Shanton and U.S. Pat. No. 5,603,996 (“the '996 patent”) to Overcash et al. The '619 patent discloses plate stock provided with a base coat which includes a styrene-acrylic polymer as well as a clay filler as a base coat as well as a top coat including another styrene acrylic polymer and another clay filler. The use of fillers is common in the art as may be seen in the '996 patent to Overcash et al. In the '996 patent a polyvinyl alcohol polymer is used together with an acrylic emulsion as well as a clay to form a barrier coating for a paperboard oven container. See Column 12, lines 50 and following. Indeed, various coatings for paper form the subject matter of many patents including the following: U.S. Pat. No. 5,981,011 to Overcash et al.; U.S. Pat. No. 5,334,449 to Bergmann et al.; U.S. Pat. No. 5,169,715 to Maubert et al.; U.S. Pat. No. 5,972,167 to Hayasaka et al.; U.S. Pat. No. 5,932,651 to Liles et al.; U.S. Pat. No. 5,869,567 to Fujita et al.; U.S. Pat. No. 5,852,166 to Gruber et al.; U.S. Pat. No. 5,830,548 to Andersen et al.; U.S. Pat. No. 5,795,923 to Janssen et al.; U.S. Pat. No. 5,770,303 to Weinert et al.; U.S. Pat. No. 4,997,682 to Coco; U.S. Pat. No. 4,609,704 to Hausman et al.; U.S. Pat. No. 4,567,099 to Van Gilder et al.; and U.S. Pat. No. 3,963,843 to Hitchmough et al.
Various methods of applying aqueous polymer coatings and smoothing them are known in the art. See U.S. Pat. No. 2,911,320 to Phillips; U.S. Pat. No. 4,078,924 to Keddie et al.; U.S. Pat. No. 4,238,533 to Pujol et al.; U.S. Pat. No. 4,503,096 to Specht; U.S. Pat. No. 4,898,752 to Cavagna et al.; U.S. Pat. No. 5,033,373 to Brendel et al.; U.S. Pat. No. 5,049,420 to Simons; U.S. Pat. No. 5,340,611 to Kustermann et al.; U.S. Pat. No. 5,609,686 to Jerry et al.; and U.S. Pat. No. 4,948,635 to Iwasaki.
Configurations for disposable food containers have been improved over the years. One configuration is shown in U.S. Pat. No. 5,088,640 (“the '640 patent”) to Littlejohn. The '640 patent discloses a disposable plate provided with a smooth outer profile which defines four radii of curvature subtending arcs of the outer portions of the plate. The various radii are selected for enhancing rigidity of the pressed paper plate as compared to other conventional designs made from the same paperboard stock. The flowing arcuate design of the '640 patent identifies additional advantages, notably with respect to manufacture. The '640 patent notes that it is possible to achieve high press speeds, exercise pleating control and maintain product consistency, even when product is formed slightly off-center due to the forgiving tolerances inherent in the design.
Another configuration for pressed paperboard food containers is disclosed in U.S. Pat. No. 5,326,020 (“the '020 patent”) to Chesire et al, The '020 patent discloses a pressed paper plate having three frustoconical or linear profiled regions about its sidewall and rim. The sidewall region includes a generally annular region flaring upwardly and outwardly from a periphery of a planar inner region and a first frustoconical, linear profiled region adjoining the annular region with the frustoconical region sloping outwardly and upwardly from the annular region. The rim region includes an outwardly flaring arcuate annular region adjoining an outer periphery of the first frustoconical region, and a second frustoconical region extending generally tangentially from the arcuate annular region. The second frustoconical or linear profiled region extends outwardly and downwardly at an angle of about 6 degrees to about 12 degrees and preferably about 6 degrees to 10.5 degrees relative to the plane defined by the planar inner region. The rim of the container further includes an outwardly and downwardly flaring frustoconical lip with a linear profile adjoining an outer periphery of the second frustoconical region in order to aid in grasping of the paperboard container by the consumer. Additionally, a plurality of radially extending mutually spaced pleats are also formed in the rim region and are internally bonded with portions of the rim region during formation of the paperboard container by a die press. Pressed paperboard containers configured in accordance with the '020 patent are capable of exhibiting very high rigidity.
Manufacturers have historically enhanced the rigidity of such circular geometry plates by increasing the thickness of the paperboard material used in such circular plates. However, increasing the thickness of the paperboard material also increases the amount of material required during manufacturing and leads to higher costs for each plate.
Therefore, there is a need for a paperboard plate with high rigidity that does not significantly increase the manufacturing costs of each plate.